1. Field of the Invention
The present invention relates to an intermediate transfer belt to be installed in an electrophotographic apparatus such as a copier or printer, a method for producing the intermediate transfer belt, and an electrophotographic apparatus using the intermediate transfer belt, and relates particularly to an intermediate transfer belt suitable for full-color image formation, and an electrophotographic apparatus using the intermediate transfer belt suitable for full-color image formation.
2. Description of the Related Art
Conventionally, for a variety of purposes, seamless belts have been used as members incorporated in electrophotographic apparatuses.
In a present-day full-color electrophotographic apparatus, in particular, the method using an intermediate transfer belt is employed, wherein developed images of four colors, i.e., yellow, magenta, cyan and black, are temporarily superimposed onto one another over an intermediate transfer medium and then transferred onto a transfer medium (such as paper) at one time.
The foregoing method using an intermediate transfer belt, conventionally used in a system in which developing devices for four colors are used with one photoconductor, is disadvantageous in that the printing speed is low. Accordingly, for high-speed printing, the four-drum tandem method is often used, wherein photoconductors for four colors are aligned and images of each color are continuously transferred to paper. However, in the four-drum tandem method, for example due to variation of paper that arises depending upon the environment, it is very difficult to secure positional accuracy for superimposition of images of each color, and consequently images with displaced colors are often formed. Accordingly, employment of the intermediate transfer method in the four-drum tandem method is becoming popular.
Under these circumstances, demands for properties (such as high-speed transfer and positional accuracy) of the intermediate transfer belt are heightening and it is becoming necessary to satisfy these demanded properties. For positional accuracy, in particular, reduction in variation caused by deformation (e.g., expansion) of the belt itself, which results from continuous use, is demanded. Also, since the intermediate transfer belt is laid out over a wide area in an apparatus and high voltage is applied thereto for image transfer, the intermediate transfer belt is required to be flame-retardant. To meet such demands, polyimide resins, polyamide-imide resins and the like, which are highly elastic, highly heat-resistant resins, are primarily used as materials for intermediate transfer belts.
It should, however, be noted that an intermediate transfer belt formed of a polyimide resin has high strength and thus high surface hardness; thus, high pressure is applied to a toner layer when a toner image is transferred, and there is local aggregation of toner, thereby possibly forming a partially non-transferred image where part of the image is not transferred. Moreover, the intermediate transfer belt is inferior in terms of its conformity to a photoconductor and to a medium (such as paper) that the intermediate transfer belt touches at a transfer section; consequently, in some cases, portions of faulty contact (empty spaces) are created at the transfer section and thus transfer unevenness may arise.
Nowadays, images are frequently formed on a variety of types of paper, using full-color electrophotography, and there are increasing occasions where types of paper varying from slippery, highly smooth paper, such as coated paper, to paper with rough surfaces, such as recycled paper, embossed paper, Japanese paper and kraft paper, are used. Conformity to such paper with different surface properties is important; poor conformity could cause paper to have color tone unevenness and shade unevenness in a concavo-convex form.
To solve the foregoing problems, a variety of intermediate transfer belts wherein a relatively flexible layer is laid over a base layer have been proposed.
In the case where a relatively flexible layer is used as a surface layer of an intermediate transfer belt, transfer pressure can be reduced and conformity to protrusions and depressions of a paper surface can be improved; however, there is a problem in that since the surface layer is inferior in releasability, toner cannot be favorably released from the surface layer, which causes a decrease in transfer efficiency, and the above favorable effects cannot be fully taken advantage of. Moreover, there is another problem in that the surface layer is inferior in abrasion resistance and scratch resistance as well.
To solve these problems, there is a method of providing a protective layer in addition to the above-mentioned layers; however, this method is unfavorable because if a material with sufficiently high transfer performance is coated with the protective layer, it is difficult for the protective layer to conform to the flexibility of a flexible layer, and thus cracks and peeling are easily caused.
Meanwhile, improvement in transferrability by attachment of fine particles to a surface has been proposed.
Japanese Patent Application Laid-Open (JP-A) No. 09-230717 proposes covering an intermediate transfer member with beads which are 3 μm or less each in diameter.
However, the formation method described in this laid-open patent application is not sufficient in terms of durability required for present-day electrophotographic apparatuses because detachment of particles arises.
JP-A Nos. 2002-162767 and 2004-354716 propose formation of a layer with the use of a material which has an affinity for hydrophobized fine particles. In these laid-open patent applications, particles having very small diameters are preferably used.
However, a thick particle layer is formed, nonuniform portions are created by aggregation of particles and there is variation in transfer performance; consequently, it is difficult to obtain an intermediate transfer belt which can help satisfy the high-level image quality that present-day electrophotographic apparatuses are required to yield.
JP-A Nos. 2007-328165 and 2009-75154 propose realizing durability by burying relatively large particles in a resin to some extent. However, in these proposals as well, the particles are present nonuniformly, and thus it is difficult to obtain an intermediate transfer belt which can help satisfy the high-level image quality that the present-day electrophotographic apparatuses are required to yield.
Silica is preferably used in all of the above-mentioned techniques in related art; note that since silica particles have strong cohesive force, it is difficult to form a uniform particle layer. Moreover, inorganic particles such as silica particles scratch the surface of an organic photoconductor suitably used as a latent image bearing member in charge of image formation, and cause the surface to be easily abraded and to decrease in durability, as the inorganic particles come into contact with the organic photoconductor at a transfer section.